Need to learn more about metals.

S

Schtik

Joined
Jul 22, 2002
Messages
133
I don't think that I completely understand the different metals.

Example:
440A is very rust-resistant and bendable.
BG-42 is very hard and can hold an edge for a very long time.

Does that mean that 440A is less likely to break under pressure than BG42?
 
Did u want a steel chart or what?
There is a brief tutorial in the faqs up at the top of th page that will help ya

ps. If u want, email me and i will send u a steel chart i got from someone in the spyderco forums. It has all the rockwell hardness figures as well as the elemnts found in each of the more common steels
 
One of our most knowledgable members, Joe Talmadge, is working on a comprehensive article on steels to be added to the FAQ area on this forum. Stayed tuned.:)
 
Schtik :

... 440A is less likely to break under pressure than BG42?
Click to expand...

BG-42 will generally be stronger, meaning it takes more force to get it to bend, however 440A is far more ductile meaning it will bend more before it breaks, and it is less likely to develop stress cracks in general (internal small breaks), becuase of its high impact toughness.

Take a butter knife and a file and bend them and note what happens. The file will be very stiff (because it is strong), but won't bend very far before it breaks violently and the pieces will tend to be straight (because it has a low ductility). The butter knife will bend rather easily (as it is much weaker), but will bend very far before it breaks if at all (because it is very ductile).

As to which makes a better prybar? You want the steel strong enough so that it is very difficult to bend, which means you get it fairly hard. But you don't make it so hard that it will snap violently with little warning. You can always straighten a bend blade, it is far harder to put pieces back together. So in general you give up a little stiffness for overall durability.

-Cliff
 
Wow is all i hafta to say. That is everythin i ever wanted a faq's on steels to say. Thanks Joe for improving an already great write up
 
The various steel alloys have different hardness and toughness characteristics, but they all have about the same modulus of elasticity. That means it takes the same force to deflect them a given amount. Cliff, the difference you note between flex qualities of a file and a butter knife are on account of different thickness.

As far as knife selection goes, thin blades are flexible and thick blades are stiff. More expensive knives with higher grade blades tend to have thicker blades. Think about a tactical ATS-34 knive versus a garden variety stainless steel Opinel. It's the blade thickness that makes the tactical knife blade stiff, not the steel.

Steel type makes a difference to how the steel responds to deflection. Low grade steels will pass their yield strength easily and permanently deform (bend). Higher grade steels will spring back straight.

The difference in thickness has an enormous affect on stiffness. It's a cube factor. Blades that are twice as thick are 8 times more stiff.

Regards, Dave
 
Originally posted by dsnw
The various steel alloys have different hardness and toughness characteristics, but they all have about the same modulus of elasticity. That means it takes the same force to deflect them a given amount. Cliff, the difference you note between flex qualities of a file and a butter knife are on account of different thickness.

As far as knife selection goes, thin blades are flexible and thick blades are stiff. More expensive knives with higher grade blades tend to have thicker blades. Think about a tactical ATS-34 knive versus a garden variety stainless steel Opinel. It's the blade thickness that makes the tactical knife blade stiff, not the steel.

Steel type makes a difference to how the steel responds to deflection. Low grade steels will pass their yield strength easily and permanently deform (bend). Higher grade steels will spring back straight.

The difference in thickness has an enormous affect on stiffness. It's a cube factor. Blades that are twice as thick are 8 times more stiff.

Regards, Dave
Click to expand...

I can't belive Cliff is letting this one go:)
 
dsnw :

The various steel alloys have different hardness and toughness characteristics, but they all have about the same modulus of elasticity. That means it takes the same force to deflect them a given amount.
Click to expand...

Only in the plastic deformation regime. Since the various cutlery steels have vastly difference yield and tensile strengths, the same load can allow you to bend various steels to vastly different points because one can pass the tensile limit (butter knife) an the other not even reach the yield point (a file).

Yes, the cross sectional areas are critical of course, but the difference in strength is as well. At an extreme example, I have put permanent bends in very thick knives (~1/2"), while being unable to even induce much of a flex in much thinner knives (1/4"), because of the huge difference in the yield points (annealed spine on the 1/2" knife, uniform hardening on the 1/4" blade).

-Cliff
 
Don't forget that quenching and tempering can make or break a knife/sword steel. Many of the cheap foreign blades suffer more from poor heat treatment than the poor quality of the steel.
 
Originally posted by jjcoolay
Did u want a steel chart or what?
There is a brief tutorial in the faqs up at the top of th page that will help ya

ps. If u want, email me and i will send u a steel chart i got from someone in the spyderco forums. It has all the rockwell hardness figures as well as the elemnts found in each of the more common steels
Click to expand...







I read you have a steel chart and am also intrested in it. If you could do me the favour and E-mail it to fechner@telus.net I'd apreciate it.
Thanx!:D
 
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